A taxonomic revision of the genus Sinotrisus Yin & Li (Coleoptera, Staphylinidae, Pselaphinae)

Abstract The genus Sinotrisus Yin & Li, comprising four species, is redefined and revised. Members of Sinotrisus are often found with ants of the subfamily Formicinae, or in humid forest habitats. The type speciesand three new species are (re-)described and illustrated: Sinotrisus kishimotoi Yin & Nomura, sp. n. (China: Sichuan), Sinotrisus nomurai Yin, Li & Zhao (type species) (China: Zhejing), Sinotrisus sinensis Yin & Nomura, sp. n. (China: Sichuan) and Sinotrisus vietnamensis Yin & Nomura, sp. n. (Vietnam: Lai Chau). A key is included as an aid to distinguishing these species.


Introduction
Batrisitae (Newton & Thayer, 1995) comprises more than 220 genera distributed in all zoogeographical regions except for New Zealand, and about one-third of them are known from Asia (Newton and Chandler 1989 and subsequent papers). The recently established genus Sinotrisus Yin & Li currently contains a single species, S. nomurai Yin, Li & Zhao, from East China (Yin et al. 2010), which is known from two males collected in a nest of the ant genus Lasius. A recent examination of the junior author's pselaphine collection revealed three new Sinotrisus species from the Oriental region. The need of a generic redefinition of Sinotrisus arose immediately after the discovery of the new species. Thus, in this paper we redefine the genus, redescribe the type species, describe the new species and provide illustrations of major diagnostic features of all species. A key is provided to assist in the identification of these species.
The terminology used here is the same as that used by Chandler (2001) in his revision of the genera of Australian Pselaphinae, except we use 'ventrite' instead of 'sternite' when concerning the meso-and metathoracic structures.
A slash (/) is used to separate lines on the same label, and a double slash (//) is used to separate different labels on the same pin.
Measurements are in millimeters; the following acronyms are used in the text: AL-length of the abdomen along the midline; AW-maximum width of the abdomen; BL-length of the body (= HL+PL+EL+AL); EL-length of the elytra along the suture; EW-maximum width of the elytra; HL-length of the head from the anterior clypeal margin to the occipital constriction; HW-width of the head across eyes; PL-length of the pronotum along the midline; PW-maximum width of the pronotum.
Material treated in this study is housed in the following public institutions: Diagnosis. Head trapezoidal; frontal rostrum low, antennal tubercles moderately raised. Pronotum with median and lateral longitudinal sulci; small antebasal spines present, lacking lateral spines; median longitudinal sulcus broadened posteriorly to form longitudinal impression, usually lacking median antebasal fovea in impression. Elytra with three basal fovea, discal striae shallow, extending to half elytral length. Tergite IV longest, with thick triangular ridge formed by inner and outer marginal carinae.
Pronotum with distinct lateral longitudinal sulci, median longitudinal sulcus ending posteriorly as broader longitudinal antebasal impression, then followed by short median carina; lateral antebasal foveae distinct; antebasal spines minute or absent, small spines variably present along discal ridges; lateral margins lacking spines; with both inner and outer pair of basolateral foveae present; paranotal carinae at least extending anteriorly to half prosternal length; lateral procoxal foveae present.
Each elytron with three distinct basal foveae, shallow discal stria extending to half elytral length; with complete sutural and marginal striae. Thorax with lateral mesoventral foveae forked, median mesoventral foveae with openings touching, into shared transverse cavity; with large mesocoxal foveae; lateral metaventral foveae present; metaventrite with narrow posteromedian notch. Legs with second and third tarsomeres subsequent in length.
Tergite IV longer than subsequent one, with inner marginal carinae extending entire tergal length, together with outer marginal carinae forming thick triangular ridge; mediobasal sulcus deep between mediobasal foveae, sulcus bracketed by short, tuberculate discal carinae; lateral foveae at mesal and lateral margins of short, deep basolateral sulci; tergite V with thin marginal carinae, punctiform mediobasal and basolateral foveae present; VI with marginal carinae indistinct, mediobasal and inner pair of basolateral foveae as shallow trace; VII with one pair of basolateral foveae and minute lateral tubercles. Sternite IV about twice length of V at midline, with large mediobasal and two pairs of small basolateral foveae; sternites V-VII each with one pair of basolateral foveae. Foveae of abdominal segments V-VII often overlapped by previous segment.
Males with vertex, apices of mesotibiae and metatrochanters modified. Aedeagus with basal bulb greatly constricted basally; paramere fused to median lobe to form ventral lobe; articulated dorsal lobe offset to right side.
Comparative notes. The genus is morphologically similar to Batrisodes Reitter of the Batrisus genus-group, but does not fit any subgeneric concept sensu Park (1951). Sinotrisus is here placed as a member of Tribasodes group by the males having protuberant metatrochanters and the aedeagus with an articulated dorsal lobe (genus-groups sensu Nomura and Idris 2003). The large genus Batrisodes holds many Asian species described by Raffray (1894) and Jeannel (1958), but at least some of these need to be re-examined and likely will be moved to other genera of the Tribasodes group (Nomura and Idris 2003;Nomura 2007). Sinotrisus shares with Intestinarius Kurbatov, Dendrolasiophilus Nomura and Majappia Nomura of the Tribasodes group the lack of the pronotal lateral spines. Intestinarius was included in the genus Batrisodes, but was later treated as a separate genus (Kurbatov 2007). Members of this genus have the head bearing three longitudinal sulci and the pronotum bearing five similar sulci, and have the aedeagus with numerous hairs at the apex of the ventral lobe. Dendrolasiophilus and Majappia seem to form a smaller group by the derived loss of characters, specifi-cally the absence of sulci on the pronotum and the frequent loss of basal elytral foveae. Dendrolasiophilus has one basal elytral fovea, and lacks elytral discal striae; Majappia has the vertexal foveae connected by a transverse sulcus, and completely lacks basal foveae on the elytra. Sinotrisus also shares with Hingstoniella the constriction of the basal portion of the aedeagus and the similar placement of the male sexual features, but the broadly triangular pronotum lacking antebasal tubercles and foveae, the presence of a large basal elytral fovea, and the lack of carinae on the margins of tergites V-VI in Hingstoniella readily separate it from Sinotrisus. Diagnosis. Vertex strongly modified in male. Antennomeres VII slightly elongate. Pronotum with minute spines along discal ridges; basolateral foveae small. Mesotibiae with apical spur longer than first tarsomeres.